The present invention relates to a frequency shift keying (FSK) code generating apparatus for data transmission and more particularly, to a FSK code generating apparatus suitable for subscriber transmission systems.
It has been known that use of AMI (alternate mark inversion) codes in data transmission requires line loss equalization, inconveniently entailing an increase in hardware. To simplify the overall system hardware, a biphase code has been proposed which does not require equalization. The biphase code assigns two states of signal opposite in phase to each of data "1" and "0", and also assigns transitions from state to state to provide a data sequence independent signal. The biphase code, however, has a drawback in that, due to higher frequency components contained therein, the system becomes susceptible to crosstalk in the transmission line and adversely affects other transmission lines nearby.